1. Field of the Invention
This invention relates to a track frame connecting structure of a heavy work vehicle.
2. Description of the Prior Art
Conventionally, as shown in FIG. 5, a body of a tractor that constitutes a heavy vehicle has a pivot shaft 31 secured thereto and track frames 4 are pivotally and tiltably mounted thereon. Crawlers 34, which are guided by rollers 35 and idlers 36, are provided on the track frames 4. Sprockets 33 are fixedly secured to sprocket shafts 32, which are disposed at a position different from the pivot shafts 31. The sprockets 33 transmit power to the crawlers 34. As shown in FIG. 6, an equalizer bar 3 has its center pivotally and tiltably mounted on the body 1 by means of a center pin 2. The equalizer bar 3 has two ends pivotally connected to the track frames 4 by means of pins 37.
Upon receiving an external force from a lateral direction, each track frame 4 has a distal end thereof (left side in the drawing) shifted toward the center of the body (toe-in) or toward the outside of the body (toe-out) around a point M in FIG. 7, which functions as its center. The equalizer bar 3 connects the left and right track frames 4 with the body 1, so as to prevent the toe-in and toe-out which may be caused by this external force. Further, as shown in FIG. 5, when the tractor travels on uneven ground, the track frames 4 tilt up and down following the landform about the pivot axis 31, thus reducing the fluctuation of the body 1.
In the above-mentioned conventional suspension system, as shown in FIG. 6, a pin 37, which connects the equalizer bar 3 and the track frame 4, traces a circular arc having a radius R and its center at center pin 2. When displaced by distance xe2x80x9cxxe2x80x9d, the pin 37 is shifted toward the inside from the initial position by the interval xcex41. When this condition is observed from the H direction shown in FIG. 5, the center line KaKa of the track frame 4 takes a position KbKb, which is displaced by xcex41 along the center line of the equalizer bar 3 around the center M of the pivot shaft 31, as shown in FIG. 7. In addition, the center of the crawler 34 deviates from the center of the sprocket 33 by xcex42 at a position where the crawler 34 is wound around the sprocket 33.
That is, the toe-in gives rise to the distortion of the alignment. Accordingly, there have been problems that non-uniform abrasion occurs at side faces of teeth of the sprockets, side faces of the crawler links, flanges of rollers and bushings of the crawlers, so that the lifetime of these parts is shortened. In addition, an excessive load is applied to the track frame and the pivot shaft frequently, so that the lifetime of these parts is also shortened.
To solve such problems, in Japanese Utility Model Laid-Open Publication 132590/1990, the applicant proposed a suspension system of a crawler type tractor that can reduce the toe-in and the toe-out by providing a crankshaft 10 and a link 20. In this arrangement, a crankshaft and a link shaft are provided where an equalizer bar 3 and a track frame 4 are connected.
This suspension system of the crawler type tractor is shown in FIG. 8 and FIG. 9. FIG. 9 is a cross-sectional view of FIG. 8 taken along a line Ixe2x80x94I. In these figures, the equalizer bar 3 is tiltably and pivotally mounted on the body 1 by means of a center pin 2. A pin journal 7 is fitted in a spherical bearing 9, which is mounted in an end portion of the equalizer bar 3. A crankshaft 10 has main journals 8 pivotally mounted in bearings 5, which are welded to the track frame 4. Levers 11 are integrally formed on both ends of the crankshaft 10. End portions of the levers 11 and brackets 22, which are fixedly secured to the frame 1, are connected by way of link pins 21 and links 20. The link pins 21 and links 20 are fixedly secured to each other. The link pins 21 and levers 11 are rotatably connected with each other, and the link pins 21 and the brackets 22 are also rotatably connected with each other.
The manner of operation of the above suspension system will now be explained. As shown in FIG. 10, the crank shaft 10 is pivotally mounted in the portion of equalizer bar 3. With the lifting of an axis Q of the bearing 5 that is brought about by the lifting of the track frame 4, an axis P of the pin journal 7 of the crank shaft 10 moves on a circular arc BB which has its center at the center pin 2. A center S of the link pins 21, which are provided at the end portions of the levers 11, moves on a circular arc CC. The levers 11 are pivotally mounted on the brackets 22 of the body 1. Accordingly, the position of the motion of the axis Q is restricted, and the motion approximates a straight line AA so that the amount of the toe-in takes the least value. Although not shown in the drawings, the similar effect is obtained in lowering the track frame 4. Accordingly, even when the track frame 4 is jolted at the time that the tractor travels on an uneven ground, an amount of toe-in caused by the equalizer bar 3 can be minimized.
However, the above-mentioned suspension system of the crawler type tractor has the following problems.
As shown in FIG. 8 and FIG. 9, the pin journals 7 provided at the end portions of the equalizer bar 3 are disposed at the outside of body 1 in the left and right directions, while the main journals 8, which are pivotally mounted on bearings 5 welded to the track frame 4, are disposed close to the center of the body 1 in the left and right directions. That is, the pin journals 7 and the main journals 8 are arranged in the left and right directions of the body. Compared to the main journals 8, which are pivotally mounted on the bearing 5 welded to the track frame 4, the pin journals 7 provided at the end portions of the equalizer bar 3 are disposed at positions further from the center pin 2. Therefore, in order to assure a necessary amount of movement of the track frame 4 in the up and down directions, it becomes necessary to have an amount of movement of the end portions of the equalizer bar 3 in the up and down directions, which is equal to or greater than the amount of movement of the track frame 4. Accordingly, it is necessary for there to be a space in the body 1, which allows such a motion of the equalizer bar 3. To this end, the center pin 2, which mounts the equalizer bar 3 to the body 1 so that the body freely tilts and pivots, must be lowered and a bracket portion 1b of the body 1, to which the center pin 2 is mounted, must be enlarged in the downward direction. The result is that the weight of the vehicle is increased and waste materials are increased, thus increasing the cost.
Further, as mentioned previously, if the track frame 4 is lifted, the axis Q of the bearing 5 has its range of motion thereof restricted and the motion substantially approximates the straight line AA. However, as mentioned previously, because the pin journals 7 are fitted in the end portions of the equalizer bar 3, the main journals 8 are pivotally mounted on the bearings 5 welded to the track frame 4 at positions toward the center of the body 1, and the axis P of the pin journal 7. Also, the axis Q of the bearing 5 and the center S of link pins 21 are arranged in the horizontal direction as shown in FIG. 8. Thus, the range of motion for the axis Q of the bearings 5 is a straight-line motion and narrow, and the range is insufficient to provide the straight-line motion in a manner necessary for a heavy work vehicle like a tractor.
The present invention was made to solve the above-mentioned problems. It is an object of the present invention to provide a track frame connecting structure of a working vehicle that can minimize the up and down movement of end portions of an equalizer bar, so that the range of the straight-line motion of the track frames is, for practical purposes, sufficient for a working vehicle like a tractor.
To achieve the above-mentioned object, a first aspect of the present invention is directed to a track frame connecting structure of a working vehicle, in which an equalizer bar is pivotally and tiltably mounted on a body by a center pin and has both end portions thereof respectively rotatably connected to connecting links. The connecting links and the track frames are rotatably connected with each other, the connecting links and one end of the limiting links are rotatably connected with each other, and the other end of the limiting links and the body are rotatably connected with each other.
LS1 is the distance between a link connecting axis S1 of the connecting link and the limiting link and a body connecting axis L connecting the limiting link and the body. The equalizer bar axis distance KP1 is the distance between an equalizer bar connecting axis P1, connecting the equalizer bar and the connecting link and the center pin axis K of the center pin. The link/equalizer bar ratio LS1/KP1 is set equal to or substantially equal to the connecting link ratio P1Q1/S1Q1. The track frame connecting distance P1Q1 is the distance between the track frame connecting axis Q1, which connects the connecting link and the track frame and the equalizer bar connecting axis P1 of the equalizer bar and the connecting link. The connecting link axis distance S1Q1 is the distance between a track frame connecting axis Q1, which connects the connecting link and the track frame, and a link connecting axis S1, which connects the connecting link and the limiting link.
The track frame connecting axis Q1, and the equalizer bar connecting axis P1 and the limiting link connecting axis S1 are arranged on a straight line. This straight line is set parallel to or substantially parallel to a body vertical center XX of the body.
According to the first aspect of the present invention, the motion of the track frame connecting axis Q1 of the track frame becomes the motion on a straight line SL of a locus shown by a dotted line in FIG. 3, due to the mechanism that sets the ratio between respective axes that are connected in the above manner to LS1/KP1=P1Q1/S1Q1. Accordingly, the motion shown by a line A1A1 that connects the track frame connecting axis Q1 (shown in FIG. 4), an axis Q10, which indicates the position of the track frame connecting axis Q1 at the time that the equalizer bar is not displaced, and axis Q12, which indicates the position of the track frame connecting axis Q1 when the track frame is lowered, is the Watt""s approximate straight-line motion (discussed later). Therefore, the track frame connecting axis Q1 moves while approximating a straight line A1A1. Further, the range within which the track frame connecting axis Q1 performs the approximate straight-line motion is sufficiently wide in practical use compared to the range obtained by the conventional suspension system of the crawler type tractor, which is proposed in Japanese Utility Model Laid-Open Publication 132590/1990. Accordingly, in both lifting and lowering of the track frame, an amount of toe-in becomes an extremely small value. Hence, the amount of toe-in, which may be generated by the equalizer bar when the track frame is tilted at the time that the heavy work vehicle travels on uneven ground, can be reduced to a sufficiently low value for practical purposes.
Eventually, the distortion of the alignment becomes extremely small, so that the lifetime of side faces of teeth of sprockets, side faces of crawler links of crawlers, flanges of rollers, bushings of the crawlers and the like is prolonged. Further, since no excessive load is applied to the track frames and a pivot shaft, the lifetime of the track frames and the pivot shaft can be prolonged.
According to a second aspect of the present invention, in a variation of the first aspect of the present invention, one of the longitudinal end portions of each of the connecting links are connected to the track frames. The other longitudinal end portions of the connecting links are connected to the limiting links, and both ends of the equalizer bar are connected to the connecting links at positions which are disposed between connecting portions. One of the longitudinal end portions of each of the connecting links is connected to the track frames and connecting portions where the other longitudinal end portions of the connecting links are connected to the limiting links.
Due to the second aspect of the present invention, in addition to the effect of the first aspect of the present invention, since the end portions of the equalizer bar and the bearings of the track frames are arranged at positions where they overlap vertically, the spaces in the left and right directions defined between the body and the equalizer bar and the tractor frame can be made small. Thus, the suspension system can be made compact in size, can be reduced in weight thereof, and can be reduced in manufacturing cost.
Further, the end portions of the equalizer bar and the bearings of the track frames are arranged at positions where they overlap vertically. This assures that the necessary amount of movement of the track frames in the vertical direction is achieved, compared to the conventional suspension system of the crawler type tractor proposed by Japanese Utility Model Laid-Open Publication 132590/1990. Thus, the amount of tilting of the equalizer bar is reduced so that it is no longer necessary to extend the bracket portion of the body to which the center pin is mounted downward, and hence the bracket portion can be made small, resulting in the reduction of both the weight of the vehicle and the manufacturing cost.
These objects and advantages of this invention will become further apparent from the following detailed explanation.